bidecadal
True.
A false rumor is floating around the Internet that this happens only once every 823 years. The reality is that it happens whenever the first day of October is on Friday, which happens on average once every seven years. The last time for this "rare" event was 6 years ago, back in 2004. And the time before that was 5 years previously, in 1999.
Every 200 years
Oh, dude, something that happens every 4 years? That's easy, man. The Olympics! It's like a massive global sports party that comes around every four years, where athletes from all over the world compete for gold medals and national pride. So yeah, mark your calendars, because the Olympics are like the ultimate every-four-years event.
An event occurring every two years is referred to as a biennial event. This pattern indicates that the event happens once every two years.
A triennial event happens every three years.
It is a triennial event. A triennial event happens three times a year.
Something that happens every six years is sexennial.
nothing
bidecadal
Semicentennial
I think you are asking about a census.
Chicago Cubs in the World Series?
Leap year
True.
the word is novennial....